Shoulder anatomybiomechanicspathomechanics

Shoulder,
anatomy,
biomechanics,
pathomechanics
By
Radhika Chintamani

CONTENTS
Functional Anatomy
Joints
Glenoid labrum anatomy
Ligaments of shoulder joint
Shoulder stability concept: static mechanism, circle concept
of instability, shoulder sleeve mechanism, dynamic stability
mechanism
Biomechanics:
a) Normal Scapulohumeral rhythm.
b) Scapulothoracic force couples.
c) Obligate translation.
 Pathomechanics

Functional anatomy
Shoulder complex is made by:
a) Sternum
b) Clavicle
c) Scapula
d) Ribs
e) Vertebrae
f) Humerus

Clavicle
Divided into lateral 1/3rd and medial 2/3rd.
Lateral part is for mobility with the UE, whereas the medial part
acts for stability
Functions:
a) Resists compressive forces
b) Stability for UE
c) Provides connection between the UE and the trunk.
 Movements of the clavicle are as follws:
a) Elevation and depression
b) Protraction and retraction
c) Upward and downward rotation

Scapula
A flat bone, with 3 borders, 2
angles, one spine and 4 fossae.
Movements occring at scapula are:
a) Elevation and depression.
b) Protraction and retraction
c) Upward and downward rotation
d) Anterior and posterior tipping
Borders: superior, medial, lateral
(medial is important in pathology
known as winging of scapula)
Angles: superior angle(important
for # of scapula, levator scapulae
insertion) inferior angle( insertion
of latissimus dorsi)

Scapula
Fossa/ glenoid fossa: articulating surface of the glenohumeral
joint. Shape=socket like. Covered by glenoid labrum.
Spine of scapula: present on dorsal surface. Divides the surface
into two parts i.e. supraspinous fossa and infraspinous fossa, and
further continues to form the acromion process.
Fossae: supraspinous fossa (origin of supraspinatus)
infraspinous fossa (infraspinatus origin), subscapular fossa
(subscapularis origin), and glenoid fossa (articulting surface for
GH joint)
17 muscles originate and insert on scapula. Clinical significance
of multiple muscle attachment: for stability as there is less
contact between the articulating surface, and also shoulder is a
3D joint, these muscles provide stability for the movement.

Function of scapula:
Provides stability for the UE during movements.
Allows 3D movement for the entire UE.

Joints
i) Sternoclavicular joint:
 Synovial sellar joint
 Only skeletal articulation between UE and axial skeleton.
 Palpable because only lower part of clavicle articulates with the
sternum whereas upper end is not.
 Capsule: lax
 Ligaments: provide stability.
a) Interclavicular lig: between two clavicles.
b) Sternoclavicular lig: between clavicle and sternum (posterior
sternoclavicular is the strongest lig)
c) Costoclavicular lig: between clavicle and first rib

ii) Acromioclavicular joint:
Synovial joint.
Lax capsule and strong lig to support.
Acromion=flat or slightly convex.
Clavicle=flat or slightly concave.
Ligs;
a) Acromioclavicular lig: limits AP trnsltn.
b) Coracoclavicular: limits supr transltn.
Conoid-Vertically orntn, taut on clavicle
rotn, Trapezoid- Horizontal orntn, resists
acromion sliding under clavicle.
c) Coracoacromial: Forms a roof on the
subacromial space, and rotator cuffs,
provides suspensory function

Prominent coracoid process: impinges subscap between
corocoid and lesser tuberosity.
Os acromiale: Unfused anterior acromial epiphysis.
Natural variance in shape of acromion:
Flat Curved Hooked
N AB AB
No space reductn,
No impingement of
RC
Slight impingement
seen of RC
Reductn in SA
space,
Impingement of RC

Evidence: .
i) According to Bigliani et al, in 1986 Frequency of
RCT varies with shape of acromion that is flat variant
has 3%, curved will have 24% whereas the hooked
shape has 73%.
ii) Acromial humeral distance would be better
pridictor of function than subscaromial space-
Mayerhoefer ME, et al, Clin J Spots Med, 2009

iii) Scapulothoracic joint:
False joint as there is no proper
articulation between scapula and thorax.
It’s a functional joint, important for 3D
motion of scapula as because of this
joint, the scapula rotates upward and
downwardly, and also tippping occurs.
Movement: in the next slide

12c
m
12c
m
12c
m
12c
m
15c
m
15c
m
15c
m
15c
m
60 deg60 deg
60 deg60 deg

Affect of Shape of Thorax on the
scapular movements:
 Due to the elliptical shape of thorax
and the position of the scapula being
on the posterior aspect, the thorax
causes scapula to tilt anteriorly as it
elevates.
 Hence during elevation there is
-------- amount of anterior tilting of
scapula.

Critical position of Glenohumeral joint:
-UPWARD ROATION
-INTERNAL ROTATION
-ADDUCTION

iv) Glenohumeral joint:
Ball and socket synovial joint.
Articulation is very unstable as humeral head articulates only
1/3rd of its articulating portion to glenoid fossa in----------
postn and 2/3rd of it articulating portion to glenoid fossa
in-------------postn .
The head faces medially, anteriorly and superiorly.
Neck shaft angle=130-150degs
Retroversion angle=20-30degs.
Glenoid fossa: placed 5deg posterior and superior inclination,
provides buttress to humeral head inferior subluxation.
Closed pack position: 90degs abduction and ER.
Open pack position: 50-70degs elevation, mild ER, 39-45degs
abduction. (Hsu, et al, JOSPT, 2002)

Arthrokinematics of GH joint
Forward elevation/Flexion:
 Humeral head slides inferiorly, rolls posteriorly, and spins
into IR.
Abduction:
 Humeral head slides inferiorly, rolls superiorly and spins
into ER.
External Rotation:
 Anterior slide and posterior roll of humeral head.

Glenoid labrum anatomy
Chock block function of glenoid labrum: makes the periphery of the
joint taller than central.
It also enhances the concavity compression provided by rotator cuff.
Increases the depth of the fossa.
Glenohumeral capsule:
Twice the surface area of humeral head; lax with inferior recess.
Very loose and redundant and will allow 2-3cm of joint surface
distraction
Shoulder shirt sleeve anamoly: redundancy of
the glenohumeral capsule to move the
shoulder joint (shoulder mobility, and
restriction in range.)

Ligaments related to Glenohumeral capsule.
a) Coarcohumeral ligament
Coracoid process to greater
tuberosity, fills space between
subscapularis and supraspinatus.
Function:
i) Counteract the force of gravity.
ii) Checks the end range ER, Flxn,
Extn.

Glenohumeral ligaments
3 distinct thickened portion of the capsule on the anterior aspect
of humeral head, named on the basis of their presence to the
humeral head and wrt each other,
a) Superior glenohumeral ligament: from glenoid labrum to lesser
tuberosity. Prevents inferior displc
b) Middle glenohumeral ligament: from anterior glenoid fossa to
antr aspct of anatomical nck. Limits ER up to 90degs of
abductn
c) Inferior glenohueral ligament complex: from ant-post-infer
glenoid to antr aspct of anatomical nck. Prevents anter subluxtn
in upper ranges of abductn. This ligament is divided into two
parts antr and postr band (along with these two bands with the
axillary pouch of the capsule forms the complex).

Combination of both CHL and SGHL:
a) Prevents inferior translatn:
 Stretched in CVAs allowing inferior subluxation when
RC inactive.
b) Limits ER when arm in dependent position:
 Contracted with adhesive capsulitis.

Shoulder stability concept.
Static mechanism:
 Bony
 Ligamentous
 Joint pressure/volumes
GHJ has a very lil inherent bony stability. Normally
translation of humeral head is 50% anterior and so as postr,
and must nt exceed the 6mm transltn from the COR during
shoulder motion.
Humeroscapular stability=Concave on convex
Scapulohumeral stability= Convex on concave.

Circle concept of instability
If one side of the joint is damaged in the GHJ, there is
high chances of the opposite getting damaged reason
being humeral head slides away the opposite direction
hitting the structure on the opposite side, that is increased
translation is possible with injury to one side of the joint,
whereas dislocation requires injury to the opposite as well.

Joint pressure and volume acting as static stabliser to
GHJ:
 Negative atmospheric pressure contributes to shoulder
stabiilty.
 Adhesion/cohension: joint surface stick together; allowing
motion but not separation.
 Limited joint volume contribute to shoulder stability.
(pathological example= adhesive capsulitis, where joint
volume is reduced leading to hypomobility).

Shoulder Stability
Theotrical
contribution
Most important
More imp
Least important
-ve Intraarticular pressure
Muscular
Capsular
Beginning of ROM Middle End

Dynamic shoulder stability
Rotator Cuff: Active contraction of these muscles centers
the GH articulation, and compressess the joint surfaces.
Force couples:
 Scapular
 Humeral
Neuromuscular Control and function: Increases dynamic
ligament tension.

Muscular innervation
Axillary nerve:
 innervates deltoid and teres minor.
 At risk: Antr instability and postr instb SX, antr GH dislocation, Prox humeral #,
rotator cuff SX.
 Ability to put hand in front jean pocket is unable to do if this nerve is damaged( teres
minor)
Long Thoracic nerve:
 Innervates serratus antr (Boxer muscle)
 At risk: chr compression or tractn, axillary inscion approach, neuritis( Parsonage-
Turner- Syndrome).
 How to evaluate: Unable to Box, Plus sign, winging scapula ( tell him to do the test
of winging scapula test, if scapula protracts=dyskinetic, if scapula wings= palsy.)
 Spinal accessory nerve:
 Innervates Trapezius.
 At risk: Direct blow, SX complication, Lymphnode biopsy.
 Checking: Unable to shrug shoulder, Flip sign.

Suprascapular nerve
Innervates: Suprspinatus, Infraspinatus?
At risk: Spinoglenoid ligament ossification, Protracted
scapula, supr or postr arthroscopy.
Test:

Biomechanical aspect
a) Sternoclavicular and Acromioclavicular Motion during
Arm- Trunk Elevation
b) Normal Scapulohumeral rhythm.
c) Scapulothoracic force couples.
d) Obligate translation.

a) Sternoclavicular and Acromioclavicular Motion during
Arm- Trunk Elevation
With the upward rotation of the scapula during arm–trunk elevation, there
must be concomitant elevation of the clavicle to which the scapula is attached.
Note that the total scapular upward rotation is 60° and the total clavicular
elevation is approximately 40°.
As the scapula is pulled away from the clavicle by upward rotation,
The conoid ligament is pulled tight and pulls on the conoid tubercle situated on
the inferior surface of the clavicle.
The tubercle is drawn toward the coracoid process, causing the clavicle to be
pulled into upward rotation.
The crank shape of the clavicle allows the clavicle to remain close to the
scapula as it completes its lateral rotation, without using additional elevation
ROM at the
sternoclavicular joint.
The sternoclavicular joint thus elevates less than its full available ROM, which
is approximately 60°.

b) Scapulohumeral rhythm
Need:
 distributes flexion motion between two joints permitting a
larger ROM with less compromise of stability.
 Maintains glenoid fossa in optimal congruency with the
humeral head and decrease shear force.
 Maintains good length tension relationship and reduces
active insufficiency.( without scapular movement abduction
occurs to about 90degs actively and 120degs passively,
difference is because that the deltoid undergoes active
insufficiency or too short to develop tension without scapular
rotation.)

b) Scapulohumeral rhythm
 Normal joint ratio:
 2:1
 GH: scapulothoracic
joint.
 Normal joint ratio:
 2:1
 GH: scapulothoracic
joint.
-Scapulothoracic joint motion formula=
30degs of Sternoclavicular motion (calvicualr elevation through base of spine
of scapula) + 30dges of acromioclavicular motion (clavicualr rotation throgh
axis at the acromioclavicular joint)= 60degs of scapulothoracic motion
-Scapulothoracic joint motion formula=
30degs of Sternoclavicular motion (calvicualr elevation through base of spine
of scapula) + 30dges of acromioclavicular motion (clavicualr rotation throgh
axis at the acromioclavicular joint)= 60degs of scapulothoracic motion

c) Scapulothoracic joint force couple
Two forces acting in opposite directions to rotate a part
about its axis of motion to rotate the scapula in AP.
Trapezius
Lower serratus antr
Scapulothoracic joint
axis being base of spine
of scapula and
movt=upward rotn till
90degs of abdctn

Force couple for upward rotation of scapula

Exactly opposite direction would be lower trap and Upper
serratus axis being= ACJ and movt= upward rotn >90degs
of abductn.
Hence;
 30-90degs of abductn powered by upp trap & lowr digitns
of serratus antr.
 90-150degs abductn powered by lower trap & upp digitns
of serratus antr.

GHJ force couple: In absence of RC’s on contractn of deltoid
during abductn, the humeral head would disclocate and supr
transltn. Both the group of muscles, act together to produce
the upward rotation of the scapula.
GH Joint
DELTOID
ROTATOR CUFFS

GH elevation force couple
Elevators- Compressor:
 Deltoid
 Pectoralis
 Supraspinatus
 Long head of biceps brachii
Depressor (elevator resistors):
 Subscapularis
 Infarspinatus
 Teres minor

Rotator cuff vectors
Suprspinatus produces a dominant
vector which provides compression
force up to 63% of total force.
Suprspinatus produces a dominant
vector which provides compression
force up to 63% of total force.
Deltoid changes its vector action as it
goes through the range of abduction,
that is at rest position deltoid vector
produces superior shear and 45% of
compressive force, but at 90degs of
abduction line of pull produces
compression
Deltoid changes its vector action as it
goes through the range of abduction,
that is at rest position deltoid vector
produces superior shear and 45% of
compressive force, but at 90degs of
abduction line of pull produces
compression

d) Capsular Obligate translation vs
Convex-Concave Morphology
Asymetrical capsular tightness causes the humeral head to
obligately translate in a side away from the tightness.
Eg: Adhesive Capsulitis: In pateints with adhesive
capsulitis, if patient complains of pain In posterior
shoulder pain, only stercthing of the tigh structures
wouldn’t releive the pain, as woud stretching+ posterior
shouder glide do, as posterior glide gives the shoulder to
move in the joint space properly thus reducing the
obligate translation.

Osteokinematic
The osteokinematics of the GH joint comprise of:
1. Flexion: the humeral head undergoes minimal superior glide (3 mm) and then
remains fixed or glides inferiorly no more than 1 mm and Normal range=0-180
2. Extension: The humeral head glides posteriorly in shoulder extension and in
lateral rotation; it translates anteriorly during abduction and medial rotation and
normal range= 0-30/40deg.
3. Abduction: normal range= 0-180deg (with Lateral rotation of humerus over
scapula; which occurs at or above 90 deg)
4. Adduction: 180-0 deg
5. Medial Rotation:0- 70 deg
6. Lateral Rotation 0-90 deg
The osteokinematics of the GH joint comprise of:
1. Flexion: the humeral head undergoes minimal superior glide (3 mm) and then
remains fixed or glides inferiorly no more than 1 mm and Normal range=0-180
2. Extension: The humeral head glides posteriorly in shoulder extension and in
lateral rotation; it translates anteriorly during abduction and medial rotation and
normal range= 0-30/40deg.
3. Abduction: normal range= 0-180deg (with Lateral rotation of humerus over
scapula; which occurs at or above 90 deg)
4. Adduction: 180-0 deg
5. Medial Rotation:0- 70 deg
6. Lateral Rotation 0-90 deg

Pathomechanics:
1. Instability
2. Impingement
3. Rotator cuff
4. Instability Impingement Rotator cuff.

Instability
TUBS
T- Traumatic, acute dislocation
U- Unilaeral (anterior and also posterior)
B- Bankrt lesion
S- Sx stabilization, or Sling.
AMBRI:
A- Atraumatic, or recurred injury.
M- Multidirectional
B- Bilateral
R- Rehabilitation
I- Inferior capsular shift.
Much
common

Methods of GN Instability classification
1. Frequency: Acute, Recurrent.
2. Degree: Subluxation, Dislocation
3. Etiology: Atraumatic, Traumatic.
4. Direction: Anterior, Posterior, Inferior, or multidirection.

Bankart Lesion Hill Sach’s Lesion
Capsular avulsion
(detachment of the capsule)
or stetch of the capsule in
the posterior part of
glenohumeral capsule,
causing the redundandancy
to migrate anteriroly and
inferiorly. Between (3 and 6
o’ clock).
• Compression fracture of
posterior humeral head
as it slips over the sharp
edge of the anterior tip of
the glenoid fossa.

Dislocation
Anterior Posterior Inferior
ABD, ER, FLEXION
PROMINENT Acromion
Loss of ER and ABD
Excessive posterior
abrasion
Avulsion # of LT (Subscap
pulling it off)
Common in overhead
activities

Impingement
1. Subacromial Impingemnet Syndrome:
A. Anterior compressive impingement= hypomobility.
B. Posterior Compressive ‘’Internal Impingement’’=
Hypermobility.
2. SLAP: Superior Labrum Anterior Posterior: creates
bigger demand on inferior capsule, causes=fall, blow,
etc. Classification by Synder:
I II III IV
Fraying of top
rim of labrum
Labrum and
biceps tendon
detach from top of
the glenoid
Bucket handle
tear of labrum
which could
droop into the
shoulder joint
Bucket handle
tear of labrum
extending into the
biceps tendon

Shoulder anatomy__biomechanics__pathomechanics

RC pathology
1. RC tear : Common muscle torn is usually supraspinatus.
 Classification:
i. Small <1cm.
ii. Medium 1-3cm.
iii. Large 3-5cm.
iv. Massive >5cm.
 Thickness of the tear: Bursal or Articular or
Intratendinous surface tear.

Snapping Scapula
If scapula is sitting lower than normal against the chest
wall, the superior medial border of the scapula may
“washboard” over the ribs, causing a snapping or clucking
sound during abduction and adduction.

SICK Scapula
Occurs due to Scapular muscle weakness.
Classified into various categories as follows;
i. Static winging: a severe form of scapular winging
occurring due to complete instability of the scapula.
Scapular winging is seen during static position as well.
ii. Dynamic winging: occurring due to only one or two
muscle weakness of the scapula. Scapular winging seen
only during movement .

SICK Scapula
Grades
S: Scapula
malposition
I: inferomedial
border
promince
C: coracoid
pain
K: dyskinesis of
scapular
movement
Grades Features
1 Prominence of Inferomedial border of the scapula
2 Prominence of entire medial border of the scapula
3 Prominence of Superomedial border of the scapula
4 Prominence of entire scapula from inferior to
superior in static position

Shoulder anatomybiomechanicspathomechanics

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